Field of the Invention
Method for taking over or receiving a sheet by a trailing edge thereof from an upline cylinder of a sheet-fed rotary printing press and transferring the sheet by the trailing edge thereof to a gripper system of a downline drum, and a transmission system for performing the method.
For inverting sheets in a rotary printing press, it has become known heretofore for a sheet transported on an upline cylinder to be grasped by the trailing edge thereof by a lifting device, such as a suction gripper, and transferred to a gripper device of a downline drum, such as an inverting drum. The trailing edge of the sheet in the region of the gripper device, within the periphery of the downline drum, by reasons of geometry, describes a shorter course than the leading edge of the sheet that is still on the upline cylinder. This leads to an unintended tautening of the sheet during the transfer; that is, the leading edge of the sheet is grasped by the gripper device of the upline cylinder at the same time as the trailing edge of the sheet is grasped by the gripper device of the downline drum.
Another problem arises when, as the sheet is taken from the upline cylinder, the holding surfaces of the suction grippers which are provided do not rest constantly on a tangent to the upline cylinder jacket surface. The latter would then execute a tilting motion relative to the sheet to be transported, which can lead to the loss of the sheet.
A great number of attempts to overcome this problem have already been disclosed in the prior art. For example, from the published German Patent Documents DE 40 12 497 C2 and DE 40 12 498 C1, It has become known to use sucker transmissions, which guide a sucker carrier with the aid of two cam-controlled rollers and enable accurate tracking of a trailing-edge sucker relative to an impression-cylinder jacket surface as the sheet is being removed. Sheet straightening or tautening and buckling are furthermore possible, but only over the direct course to the inverting gripper of the downline drum. The cam segments for controlling the sucker transmission are secured to the inverting drum. The use of multiple-size inverting drums with a plurality of transport systems leads to a large number of cam segments which, on the one hand, for production reasons, are vulnerable to error, and cannot be adjusted to one another without error even if the individual cam segments are adjusted in a complex and costly manner. As a consequence, the trailing edge of the sheet has different transport paths, which leads to rhythmical transfer errors of the sheets, with resultant undesired doubling phenomena.
The published German Patent Document DE 196 17 545 C1 shows a sucker transmission through the intermediary of a crank, namely a combination of a rocker and a coupling link, which is unable to execute the takeover of sheets from the printing cylinder at a constant tangent. This means that the portion of the sheet that is free of the suction surface or has already been taken over is not located at all times on a tangent to the printing cylinder jacket face. Especially with heavy paper, such as cardboard, this provision can lead to the loss of the sheet.
The published German Patent Document DE 196 17 493 A1 shows a sucker guide through the intermediary of revolving wheel transmissions, but this is still unable to maintain the desired constancy of the tangent.
The published German Patent Documents DD-WP 110 452, DE 196 17 542 A1, DE 196 17 543 A1 and DE 196 17 544 C1 show four and five-linkage transmissions for guiding the suction devices. However, these transmissions are incapable of executing a constant-tangent sheet removal from the upline cylinder, nor is a purposeful tautening or bulging of the sheet after sheet removal possible, especially with the four-link mechanisms.
It is accordingly an object of the invention to provide a method by which a sheet can be taken over by its trailing edge from an upline cylinder for the purpose of inverting and transferring the sheet without jolting to a downline cylinder, in which the trailing edge of the sheet, until a firm gripper lock takes place, is to be guided at a constant tangent to a forward sheet region contacting the upline cylinder, and to provide a transmission system for performing the method.
With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, a method for taking over a sheet by a trailing edge thereof from an upline cylinder of a sheet-fed rotary printing press and transferring the sheet by the trailing edge thereof to a gripper system, by placing a suction gripper on the sheet in a marginal region of the trailing edge and, during the sheet takeover, having the suction gripper follow the periphery of the upline cylinder, having the suction gripper guided at a constant tangent into the periphery of a downline inverting drum and, along this course, having the suction gripper execute a relative motion in the direction of the tangent so as to tauten the sheet, which comprises, upon reaching a transfer position at the gripper system, having the suction gripper execute a relative motion in the sheet transport direction and, when the grippers close, having the suction gripper and the gripper system disposed at rest relative to one another.
In accordance with another aspect of the invention, there is provided a transmission system on an inverting drum of a sheet-fed rotary printing press for guiding a retaining element for a trailing edge of a sheet, comprising three mutually coupled drive systems controllable independently of one another for generating a path of motion of the retaining element.
In accordance with a further feature of the invention, each of the drive systems includes a roller lever embodied as a rocker swivellably supported on the inverting drum.
In accordance with an added feature of the invention, the rockers have respective control rollers operatively engageable with stationary control cams.
In accordance with an additional feature of the invention, the transmission system includes a sucker carrier guidable by a crank and a coupling link.
In accordance with yet another feature of the invention, the coupling link has three articulating joints, and each of the articulating joints is connected to one of the drive systems.
In accordance with yet a further feature of the invention, the coupling link is guided by a crank and the rocker, and is connected at one of the articulating joints to the sucker carrier.
In accordance with yet an added feature of the invention, the rocker has a toothed quadrant meshing with a toothed quadrant of the coupling link, and two of the rockers have a common bearing point.
In accordance with yet an additional feature of the invention, the system is disposed multiply along the axial length of the inverting drum.
In accordance with an alternate feature of the invention, a cylinder is disposed upline of the inverting drum, and the system is disposed multiply along the axial length of the cylinder.
In accordance with a concomitant mode of the method of the invention, the gripper system is formed of inverting grippers on the downline inverting drum and, when a transfer position is reached at the inverting grippers, the suction gripper is caused to execute the relative motion in the sheet transport direction, and the suction gripper and the inverting grippers are disposed at rest relative to one another when the grippers close.
It is an advantage of the invention that the sheet is transferrable at a constant tangent to the gripper device of the inverting drum.
By the transmission according to the invention, the trailing edge of the sheet can be guided along the gripper pad of the inverting drum gripper at a relative speed, so that the sheet is caused to bulge in an intended manner. The resultant bellying of the sheet counteracts a geometrically dictated tautening of the sheet. Consequently, the transfer of the trailing edge of the sheet to the inverting gripper takes place without tension or jolting.
Adjustment is made considerably shorter and easier by disposing the cam segments for controlling the sucker transmission in a stationary manner. Particularly when inverting drums multiply larger are used, with a plurality of sucker systems distributed over the circumference, each sucker system is controlled by a common cam. This provision minimizes rhythmical transfer errors.
Doubling caused by transfer errors upon inversion is advantageously prevented. The quality of the printing is improved. Two exemplary embodiments are shown in the drawings and are described hereinbelow.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for taking over a sheet by a trailing edge thereof from an upline cylinder of a sheet-fed rotary printing press, and a transmission system for performing the method, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: